This page lists various Xen related development projects that can be picked up by anyone! If you're interesting in hacking Xen this is the place to start! Ready for the challenge?

To work on a project:

Find a project that looks interesting (or a bug if you want to start with something simple)

Send an email to xen-devel mailinglist and let us know you started working on a specific project.

Post your ideas, questions, RFCs to xen-devel sooner than later so you can get comments and feedback.

Send patches to xen-devel early for review so you can get feedback and be sure you're going into correct direction.

Your work should be based on xen-unstable development tree, if it's Xen and/or tools related. After your patch has been merged to xen-unstable it can be backported to stable branches (Xen 4.2, Xen 4.1, etc).

If you have new ideas, suggestions or development plans let us know and we'll update this list!

List of projects

Domain support

Utilize Intel QuickPath on network and block path.

Date of insert: 01/22/2013; Verified: Not updated in 2016; GSoC: Yes

Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Difficulty: High

Skills Needed: The basic requirement for this project is Linux kernel programming skill.
The candidate for this project should be familiar with open source development workflow as it may require collaboration with several parties.

Description: The Intel QuickPath, also known as Direct Cache Access, is the chipset that sits in the PCIe subsystem in the Intel systems. It allows the PCIe subsystem to tag which PCIe writes to memory should reside in the Last Level Cache (LLC, also known as L3, which in some cases can be of 15MB or 2.5MB per CPU). This offers incredible boosts of speed - as we bypass the DIMMs and instead the CPU can process the data in the cache.
Adding this component in the network or block backends can mean that we can keep the data longer in the cache and the guest can process the data right off the cache.

Description: VirtIO provides a 9P FS transport, which is essentially a paravirt file system device. VMs can mount arbitrary file system hierarchies exposed by the backend. The 9P FS specification has been around for a while, while the VirtIO transport is relatively new. The project would consist of implementing a classic Xen front/back pv driver pair to provide a transport for the 9P FS Protocol.

OVMF Compatibility Support Module support in Xen

Date of insert: 2/5/2014; Verified: Not updated in 2016; GSoC: Yes

Technical contact: Wei Liu <wei.liu2@citrix.com>

Difficulty: Easy

Skills Needed: Unknown

Description: Currently Xen supports booting HVM guest with Seabios and OVMF UEFI firmware, but those are separate binaries. OVMF supports adding legacy BIOS blob in its binary with Compatibility Support Module support. We can try to produce single OVMF binary with Seabios in it, thus having only one firmware binary.

Tasks may include:

figure out how CSM works

design / implement interface between Hvmloader and the unified binary

Outcomes: Not specified, project outcomes

Improvements to firmware handling HVM guests

Date of insert: 07/16/2015; Verified: Not updated in 2016; GSoC: Yes

Technical contact: Andrew Cooper <andrew.cooper3@citrix.com>

Difficulty: Easy

Skills Needed: Unknown

Description: Currently, all firmware is compiled into HVMLoader.

This works, but is awkward when used using a single distro seabios/ovmf designed for general use. In such a case, any time an update to seabios/ovmf happens, hvmloader must be rebuilt.

The purpose of this project is to alter hvmloader to take firmware blobs as a multiboot module rather than requiring them to be built in. This reduces the burden of looking after Xen in a distro environment, and will also be useful for developers wanting to work with multiple versions of firmware.

As an extension, support loading an OVMF NVRAM blob. This enabled EFI NVRAM support for guests.

Outcomes: Not specified, project outcomes

Hypervisor

Introducing PowerClamp-like driver for Xen

Date of insert: 01/22/2013; Verified: Not updated in 2016; GSoC: Yes

Technical contact: George Dunlap <george.dunlap@eu.citrix.com>

Difficulty: Unknown

Skills Needed: Unknown

Description: PowerClamp was introduced to Linux in late 2012 in order to allow users to set a system-wide maximum

power usage limit. This is particularly useful for data centers, where there may be a need to
reduce power consumption based on availability of electricity or cooling. A more complete writeup
is available at LWN.

These same arguments apply to Xen. The purpose of this project would be to implement a similar functionality in Xen,
and to make it interface as well as possible with the Linux PowerClamp tools, so that the same tools could be used

Description: NUMA (Non-Uniform Memory Access) systems are advanced server platforms, comprising multiple nodes. Each node contains processors and memory. An advanced memory controller allows a node to use memory from all other nodes, but that happens, data transfer is slower than accessing local memory. Memory access times are not uniform and depend on the location of the memory and the node from which it is accessed, hence the name.

Trascendent memory (Tmem) can be seen as a mechanism for discriminating between frequently and infrequently used data, and thus helping allocating them properly. It would be interesting to investigate and implement all the necessary mechanisms to take advantage of this and improve performances of Tmem enabled guests running on NUMA machines.

For instance, implementing something like alloc_page_on_any_node_but_the_current_one() (or any_node_except_this_guests_node_set() for multinode guests), and have Xen's Tmem implementation use it (especially in combination with selfballooning), could solve a significant part of the NUMA problem when running Tmem-enabled guests.

Outcomes: Not specified, project outcomes

Userspace Tools

Refactor Linux hotplug scripts

Description: Current Linux hotplug scripts are all entangled, which makes them really difficult to understand or modify. The reason of hotplug scripts is to give end-users the chance to "easily" support different configuration for Xen devices.

Linux hotplug scripts should be analized, providing a good description of what each hotplug script is doing. After this, scripts should be cleaned, putting common pieces of code in shared files across all scripts. A Coding style should be applied to all of them when the refactoring is finished.

XL to XCP VM motion

Description: Currently xl (the toolstack supplied alongside Xen) and xapi (the XCP toolstack) have very different concepts about domain configuration, disk image storage etc. In the XCP model domain configuration is persistent and stored in a data base while under xl domain configuration is written in configuration files. Likewise disk images are stored as VDIs in Storage Repositories while under xl disk images are simply files or devices in the dom0 filesystem. For more information on xl see XL. For more information on XCP see XCP Overview.

This project is to produce one or more command-line tools which support migrating VMs between these toolstacks.

One tool should be provided which takes an xl configuration file and details of an XCP pool. Using the XenAPI XML/RPC interface It should create a VM in the pool with a close approximation of the same configuration and stream the configured disk image into a selected Storage Repository.

A second tool should be provided which performs the opposite operation, i.e. give a reference to a VM residing in an XCP pool it should produce an XL compatible configuration file and stream the disk image(s) our of Xapi into a suitable format.

These tools could be reasonably bundled as part of either toolstack and by implication could be written in either C, Ocaml or some other suitable language.

The tool need not operate on a live VM but that could be considered a stretch goal.

An acceptable alternative to the proposed implementation would be to implement a tool which converts between a commonly used VM container format which is supported by XCP (perhaps OVF or similar) and the xl toolstack configuration file and disk image formats.

Allowing guests to boot with a passed-through GPU as the primary display

Date of insert: 01/22/2013; Verified: Not updated in 2016; GSoC: Yes

Technical contact: George Dunlap <george.dunlap@eu.citrix.com>

Difficulty: Unknown

Skills Needed: Unknown

Description: One of the primary drivers of Xen in the "consumer market" of the open-source world is the ability to

pass through GPUs to guests -- allowing people to run Linux as their main desktop but easily play
games requiring proprietary operating systems without rebooting.

GPUs can be easily passed through to guests as secondary displays, but as of yet cannot be passed
through as primary displays. The main reason is the lack of ability to load the VGA BIOS from the card into the guest.

The purpose of this project would be to allow HVM guests to load the physical card's VGA bios, so that the guest can
boot with it as the primary display.

Advanced Scheduling Parameters

Description: The credit scheduler provides a range of "knobs" to control guest behavior, including CPU weight and caps. However,

a number of users have requested the ability to encode more advanced scheduling logic. For instance, "Let this VM max out for 5 minutes out of any given hour; but after that, impose a cap of 20%, so that even if the system is idle he can't an unlimited amount of CPU power without paying for a higher level of service."

This is too coarse-grained to do inside the hypervisor; a user-space tool would be sufficient. The goal of this project would

be to come up with a good way for admins to support these kinds of complex policies in a simple and robust way.

Description: It is often useful in debugging kernel, hypervisor or performance problems to understand the bus topology of a server. This project will create a layout diagram for a server automatically using data from ACPI Tables, SMBios Tables, lspci output etc. This tool would be useful in general Linux environments including Xen and KVM based virtualisation systems.
There are many avenues for extension such as labelling relevant hardware errata, performing bus throughput calculations etc.

Outcomes: A tool is created that can either run on a live Linux system or offline using captured data to produce a graphical representation of the hardware topology of the system including bus topology, hardware device locations, memory bank locations, etc. The tool would be submitted to a suitable open-source project such as the Xen hypervisor project or XCP.

kdd allows you to debug a running Windows virtual machine on Xen using standard Windows kernel debugging tools like WinDbg. kdd is an external debugger stub for the windows kernel.
Windows can be debugged without enabling the debugger stub inside windows kernel by using kdd. This is important for debugging hard to reproduce problems on Windows virtual machines that may not have debugging enabled.

Nice to have: Allow kdd to operate on a Windows domain checkpoint file (output of xl save for e.g.)

Outcomes: Code is submitted to xen-devel@xen.org for inclusion in the xen-unstable project.

Lazy restore using memory paging

Date of insert: 01/20/2014; Verified: Not updated in 2016; GSoC: Yes

Technical contact: Andres Lagar-Cavilla <andres@lagarcavilla.org>

Difficulty: Unknown

Skills Needed: A good understanding of save/restore, and virtualized memory management (e.g. EPT, shadow page tables, etc). In principle the entire project can be implemented in user-space C code, but it may be the case that new hypercalls are needed for performance reasons.

Description: VM Save/restore results in a boatload of IO and non-trivial downtime as the entire memory footprint of a VM is read from IO.

Xen memory paging support in x86 is now mature enough to allow for lazy restore, whereby the footprint of a VM is backfilled while the VM executes. If the VM hits a page not yet present, it is eagerly paged in.

There has been some concern recently about the lack of docs and/or mature tools that use xen-paging. This is a good way to address the problem.

Outcomes: Expected outcome:

Mainline patches for libxc and libxl

CPUID Programming for Humans

Date of insert: 02/04/2014; Verified: Not updated in 2016; GSoC: Yes

Technical contact: Andres Lagar-Cavilla <andres@lagarcavilla.org>

Difficulty: Unknown

Skills Needed: A good understanding of C user-land programming, and the ability to dive into qemu/libvirt (for reference code and integration), as well as libxc and libxl (for implementation).

Description: When creating a VM, a policy is applied to mask certain CPUID features. Right now it's black magic.

THe KVM stack has done an excellent job of making this human-useable, and understandable.

And in <qemu>/target-i386.c you find a fairly comprehensive description of x86 processor models, what CPUID features are inherent, and what CPUID feature each of these symbolic flags enables.

In the Xen world, there is a libxc interface to do the same, although it's all hex and register driven. It's effective, yet horrible to use.

An ideal outcome would have libxl config files and command line absorb a similarly human-friendly description of the CPUID features a user wishes for the VM, and interface appropriately with libxl. Further, autodetection of best CPUID shuold yield a human-readable output to be able to easily understand what the VM thinks about its processor.

Mirage and XAPI projects

There are separate wiki pages about XCP and XAPI related projects. Make sure you check these out aswell!

Create a tiny VM for easy load testing

Date of insert: 01/30/2013; Verified: Not updated in 2016; GSoC: yes

Technical contact: Dave Scott <first.last@citrix.com>

Difficulty: Medium

Skills Needed: OCaml

Description: The http://www.openmirage.org/ framework can be used to create tiny 'exokernels': entire software stacks which run directly on the xen hypervisor. These VMs have such a small memory footprint (16 MiB or less) that many of them can be run even on relatively small hosts. The goal of this project is to create a specific 'exokernel' that can be configured to generate a specific I/O pattern, and to create configurations that mimic the boot sequence of Linux and Windows guests. The resulting exokernel will then enable cheap system load testing.

The first task is to generate an I/O trace from a VM. For this we could use 'xen-disk', a userspace Mirage application which acts as a block backend for xen guests (see http://openmirage.org/wiki/xen-synthesize-virtual-disk). Following the wiki instructions we could modify a 'file' backend to log the request timestamps, offsets, buffer lengths.

The second task is to create a simple kernel based on one of the MirageOS examples (see http://github.com/mirage/mirage-skeleton). The 'basic_block' example shows how reads and writes are done. The previously-generated log could be statically compiled into the kernel and executed to generate load.

Fuzz testing Xen with Mirage

Date of insert: 28/11/2012; Verified: Not updated in 2016; GSoC: yes

Technical contact: Anil Madhavapeddy <anil@recoil.org>

Difficulty: medium

Skills Needed: OCaml

Description: MirageOS (http://openmirage.org) is a type-safe exokernel written in OCaml which generates highly specialised "appliance" VMs that run directly on Xen without requiring an intervening guest kernel. We would like to use the Mirage/Xen libraries to fuzz test all levels of a typical cloud toolstack. Mirage has low-level bindings for Xen hypercalls, mid-level bindings for domain management, and high-level bindings to XCP for cluster management. This project would build a QuickCheck-style fuzzing mechanism that would perform millions of random operations against a real cluster, and identify bugs with useful backtraces.

The first task would be to become familiar with a specification-based testing tool like Kaputt (see http://kaputt.x9c.fr/). The second task would be to choose an interface for testing; perhaps one of the hypercall ones.

Outcomes: 1. a repo containing a fuzz testing tool; 2. some unexpected behaviour with a backtrace (NB it's not required that we find a critical bug, we just need to show the approach works)

From simulation to emulation to production: self-scaling apps

Date of insert: 28/11/2012; Verified: Not updated in 2016; GSoC: no, too much work

Technical contact: Anil Madhavapeddy <anil@recoil.org>

Difficulty: hard

Skills Needed: OCaml

Description: MirageOS (http://openmirage.org) is a type-safe exokernel written in OCaml which generates highly specialised "appliance" VMs that run directly on Xen without requiring an intervening guest kernel. An interesting consequence of programming Mirage applications in a functional language is that the device drivers can be substituted with emulated equivalents. Therefore, it should be possible to test an application under extreme load conditions as a simulation, and then recompile the *same* code into production. The simulation can inject faults and test data structures under distributed conditions, but using a fraction of the resources required for a real deployment.

The first task is to familiarise yourself with a typical Mirage application, I suggest a webserver (see https://github.com/mirage/mirage-www). The second task is to replace the ethernet driver with a synthetic equivalent, so we can feed it simulated traffic. Third, we should inject simulated web traffic (recorded from a real session) and attempt to determine how the application response time varies with load (number of connections; incoming packet rate).

This project will require a solid grasp of distributed protocols, and functional programming. Okasaki's book will be a useful resource...

Outcomes: 1. a repo/branch with a fake ethernet device and a traffic simulator; 2. an interesting performance graph

Towards a multi-language unikernel substrate for Xen

Description: There are several languages available that compile directly to Xen microkernels, instead of running under an intervening guest OS. We're dubbing such specialised binaries as "unikernels". Examples include:

Each of these is in a different state of reliability and usability. We would like to survey all of them, build some common representative benchmarks to evaluate them, and build a common toolchain based on XCP that will make it easier to share code across such efforts. This project will require a reasonable grasp of several programming languages and runtimes, and should be an excellent project to learn more about the innards of popular languages.

DRBD Integration

Description: DRBD is potentially a great addition to the other high-availability features in XenAPI. An architecture of as few as two Dom0s with DRBD mirrored local storage is an inexpensive minimal HA configuration enabling live migration of VMs between physical hosts and providing failover in case of disk failure, and eliminates the need for external storage. This setup can be used in small shop or hobbyist environments, or could be used as a basic unit in a much larger scalable architecture.

Existing attempts at integrating DRBD sit below the SM layer and thus do not enable one VBD per DRBD device. They also suffer from a split-brain situation that could be avoided by controlling active/standby status from XenAPI.

DRBD should be implemented as a new SR type on top of LVM. The tools for managing DRBD devices need to be built into storage management, along with the logic for switching the active and standby nodes.